CODEWITHSUNDEEP
javabigdecimalfloorceil
Milan Desai
Milan Desai

Reputation: 1306

Why Does java BigDecimal division results different than Double division when using RoundingMode

I have been working on a tolerance calculation code written in Double, having precisions and rounding issues I decided to move on to BigDecimal considering it's more precise and less likely to encounter rounding issue. In a calculation, piece of code uses Math.floor() and Math.Ceil when dividing values.

Strange observation that ROUNDING_MODE.floor and ceil does not actually apply when using BigDecimal, here's the minimal re-producable example.

Double doubleFloor = Math.floor(5.5/1.0);
Double doubleCeil = Math.ceil(5.5/1.0);
System.out.println(doubleFloor);
System.out.println(doubleCeil);  
    
BigDecimal bigDecimalFloor = BigDecimal.valueOf(5.5).divide(BigDecimal.ONE,1,RoundingMode.FLOOR);
BigDecimal bigDecimalCeil = BigDecimal.valueOf(5.5).divide(BigDecimal.ONE,1,RoundingMode.CEILING);
System.out.println(bigDecimalFloor);
System.out.println(bigDecimalCeil);

I'd expect to print identical value for such small division however I get following, floor and ceil does not seem to be calculated as expected.

5.0
6.0
5.5
5.5

What is it that I am missing. ?

Thank you in Advance

Upvotes: 0

Views: 418

Answers (1)

Andy Turner
Andy Turner

Reputation: 140299

To quote the Javadoc

If rounding must be performed to generate a result with the specified scale, the specified rounding mode is applied.

5.5 doesn't need to be rounded when the scale is 1, so the rounding mode isn't applied.

It would work like Math.floor and Math.ceil if the scale were 0:

BigDecimal bigDecimalFloor = BigDecimal.valueOf(5.5).divide(BigDecimal.ONE,0,RoundingMode.FLOOR);
BigDecimal bigDecimalCeil = BigDecimal.valueOf(5.5).divide(BigDecimal.ONE,0,RoundingMode.CEILING);
System.out.println(bigDecimalFloor);
System.out.println(bigDecimalCeil);

Output

5
6

Upvotes: 5

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